<template>
  <div class="list">
    <ul>
      <li class="item"
          v-for="item of letters"
          :key="item"
          :ref="item"
          @touchstart.prevent="handleTouchStart"
          @touchmove="handleTouchMove"
          @touchend="handleTouchEnd"
          @click="handleLetter"
      >
        {{item}}
      </li>
    </ul>
  </div>
</template>

<script>
  export default {
    name: "CityAlphabet",
    props: {
      cities: Object
    },
    data(){
      return{
        touchStart:false,
        startY:0,
        timer:null
      }
    },updated(){
      const startY = this.$refs['A'][0].offsetTop
    },
    computed:{
      letters(){
        const letters = []
        for (let i in this.cities){
          letters.push(i)
        }
        return letters
      }
    },
    methods: {
      handleLetter(e) {
        this.$emit('change', e.target.innerText)
      },
      handleTouchStart() {
        this.touchStart = true
      },
      handleTouchMove(e) {
        if (this.touchStart){
          if (this.timer){
            clearTimeout(this.timer)
          } this.timer = setTimeout(()=>{
            const touchy = e.touches[0].clientY - 79;
            const index = Math.floor((touchy - this.startY) / 20);
            if (index >= 0 && index <this.letters.length){
              this.$emit('change',this.letters[index])
            }
          },20)

        }
      },
      handleTouchEnd() {
        this.touchStart = false
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~styles/varibles.styl";
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    right 0
    top: 1.58rem
    bottom 0
    width .4rem
    touch-action: none;

    .item
      text-align center
      line-height .4rem
      color $bgColor

</style>
